1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to contact magnetic printing used to create magnetic patterns on magnetic recording media.
2. Description of the Related Art
Conventional disc drives use magnetic properties of materials to store and retrieve data. Typically, disc drives are incorporated into electronic equipment, such as computer systems and home entertainment equipment, to store large amounts of data in a form that can be quickly and reliably retrieved. The major components of a disc drive include magnetic media in the form of a disk, read-write heads, a motor and software. The magnetic media is rotated by a motor at a constant high speed while the read-write head, which rests on a head gimble assembly, glides over the magnetic media reading and writing signals to the media. The surface of each magnetic media is divided into a series of data tracks, which are radially spaced apart and which extend circumferentially around the magnetic media disc. The data tracks store data in the form of magnetic flux transitions within the radial extent of the tracks on the disc surfaces.
Typically, each data track is divided into a number of data sectors that store fixed sized blocks of user data. Embedded among the sectors on each track are servo fields that enable the disc drive to control the position of heads used to transfer the user data between the discs and a host computer. More particularly, the heads are mounted to a rotary actuator assembly which includes a coil of a voice coil motor, so that the position of the heads relative to the tracks can be maintained by the application of current to the coil by a closed loop digital servo system in response to the servo information read by the servo fields.
The servo fields are written to the discs during the manufacture of the disc drives using an extremely precise servo track writer as illustrated in FIG. 1A. Conventional servo track writers include an anti-vibration table 110, a recording media 115, a spindle motor with a hub 120, which rotates the media in a direction 125, a read-write head 130, an arm 135 and a controller 140. Anti-vibration table 110 is a conventional table designed to reduce vibration. Spindle motor with hub 120 rotates recording media 115 at a constant rate while read-write head 130 reads and writes servo signals to recording media 115. Read-write head 130 is attached to an arm 135 which driven by controller 140. Controller 140 contains a laser based positioning system which moves arm 135 by receiving feedback from a closed loop detection system and engaging an actuator assembly that advances the position of the read-write head to the servo writing position. Additionally, controller 140 includes control circuitry for providing servo information to be stored in the servo fields. Since servo fields are used to define tracks, precise control and positioning of the read-write head is required during the servo field writing to the recording media 115 surface.
The typical manufacturing process of magnetic disk with a servo pattern in illustrated in FIG. 1B. In a first step 150, a disk is prepared for sputtering by being textured and cleaned. Next in step 155, various layers including a magnetic layer and a protective layer are deposited on top of the disk. The magnetic layer usually consists of a cobalt based alloy and is used to record information via magnetic signals whereas the protective layer usually consists of a diamond like carbon layer. Next in step 160, a lube layer is deposited over the media with the magnetic layer. In step 165, the lubed disked undergoes a buff process wherein the media is smoothed by rubbing a pad over the top of the surface. After being buffed, the media is glide tested in step 170 for defects that could cause a head to crash thereon. Next in step 175, the media is certified by writing signals to it and reading signals from it. Typically, after certification is done in step 175 the media is shipped to a hard drive building facility where it is servo formatted and installed into a hard drive. The servo formatting is then done in step 180 with a conventional servo writer as was discussed with reference to FIG. 1A above. Finally, in step 185 the disk is tested again and installed into a finished hard drive.
In order to facilitate reliable operation of the disc drive, proper radial alignment of the servo fields is essential. If errors are introduced in the placement of the servo fields, position error signals (PES) generated by the servo system during subsequent operation of the drive are detected at corresponding frequencies. The PES is a measure of the relative position of a selected head with respect to an associated track and is used primarily during track following operations to maintain the head over the center of the track. Frequency dependent PES for a given track result in the repeated adjustment of the position of the head by the servo system in an attempt to maintain the head over the center of the track during each revolution of the disc. When such frequencies are sufficiently severe, the correction required to account for these frequencies can require a significant amount of correction limiting the overall track density that can be achieved in a disc drive design. One source of error that occurs during the servo writer process is the spindle motor, which includes bearing assemblies with characteristic frequencies that are generated from the rotation of the balls and ball cages within the inner and outer bearing raceways. These bearing frequencies can result in low frequency errors being laid down in the servo pattern.
Accordingly, there is a need for an improved servo writer system and method that permits the writing of servo patterns early on in the process while reducing the number of servo data errors written to discs of a disc drive.